ORCID Profile
0000-0002-6730-3298
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Astronomical and Space Sciences | General Relativity and Gravitational Waves | Cosmology and Extragalactic Astronomy | Astronomical and Space Instrumentation
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in the Information and Computing Sciences |
Publisher: American Astronomical Society
Date: 10-01-2019
Publisher: American Astronomical Society
Date: 21-12-2020
Publisher: American Astronomical Society
Date: 21-12-2020
Publisher: American Astronomical Society
Date: 06-2021
Publisher: Oxford University Press (OUP)
Date: 15-02-2021
Abstract: We describe the ongoing Relativistic Binary programme (RelBin), a part of the MeerTime large survey project with the MeerKAT radio telescope. RelBin is primarily focused on observations of relativistic effects in binary pulsars to enable measurements of neutron star masses and tests of theories of gravity. We selected 25 pulsars as an initial high priority list of targets based on their characteristics and observational history with other telescopes. In this paper, we provide an outline of the programme, and present polarization calibrated pulse profiles for all selected pulsars as a reference catalogue along with updated dispersion measures. We report Faraday rotation measures for 24 pulsars, twelve of which have been measured for the first time. More than a third of our selected pulsars show a flat position angle swing confirming earlier observations. We demonstrate the ability of the Rotating Vector Model, fitted here to seven binary pulsars, including the Double Pulsar (PSR J0737–3039A), to obtain information about the orbital inclination angle. We present a high time resolution light curve of the eclipse of PSR J0737–3039A by the companion’s magnetosphere, a high-phase-resolution position angle swing for PSR J1141–6545, an improved detection of the Shapiro delay of PSR J1811–2405, and pulse scattering measurements for PSRs J1227–6208, J1757–1854, and J1811–1736. Finally, we demonstrate that timing observations with MeerKAT improve on existing data sets by a factor of, typically, 2–3, sometimes by an order of magnitude.
Publisher: American Physical Society (APS)
Date: 15-12-2021
Publisher: American Astronomical Society
Date: 09-04-0077
Publisher: Oxford University Press (OUP)
Date: 12-12-2022
Abstract: We present the first 2.5 yr of data from the MeerKAT Pulsar Timing Array (MPTA), part of MeerTime, a MeerKAT Large Survey Project. The MPTA aims to precisely measure pulse arrival times from an ensemble of 88 pulsars visible from the Southern hemisphere, with the goal of contributing to the search, detection, and study of nanohertz-frequency gravitational waves as part of the International Pulsar Timing Array. This project makes use of the MeerKAT telescope and operates with a typical observing cadence of 2 weeks using the L-band receiver that records data from 856 to 1712 MHz. We provide a comprehensive description of the observing system, software, and pipelines used and developed for the MeerTime project. The data products made available as part of this data release are from the 78 pulsars that had at least 30 observations between the start of the MeerTime programme in February 2019 and October 2021. These include both sub-banded and band-averaged arrival times and the initial timing ephemerides, noise models, and the frequency-dependent standard templates (portraits) used to derive pulse arrival times. After accounting for detected noise processes in the data, the frequency-averaged residuals of 67 of the pulsars achieved a root-mean-square residual precision of $\\lt 1 \\, \\mu \\rm {s}$. We also present a novel recovery of the clock correction waveform solely from pulsar timing residuals and an exploration into preliminary findings of interest to the international pulsar timing community. The arrival times, standards, and full Stokes parameter-calibrated pulsar timing archives are publicly available.
Publisher: American Astronomical Society
Date: 17-12-2019
Publisher: American Physical Society (APS)
Date: 05-11-2018
Publisher: Springer Science and Business Media LLC
Date: 16-09-2019
Publisher: Oxford University Press (OUP)
Date: 02-05-2019
Publisher: Oxford University Press (OUP)
Date: 02-01-2023
Abstract: Precision timing of millisecond pulsars (MSPs) in binary systems enables observers to detect the relativistic Shapiro delay induced by space–time curvature. When favourably aligned, this enables constraints to be placed on the component masses and system orientation. Here, we present the results of timing c aigns on seven binary MSPs observed with the 64-antenna MeerKAT radio telescope that show evidence of Shapiro delay: PSRs J0101−6422, J1101−6424, J1125−6014, J1514−4946, J1614−2230, J1732−5049, and J1909−3744. Evidence for Shapiro delay was found in all of the systems, and for three the orientations and data quality enabled strong constraints on their orbital inclinations and component masses. For PSRs J1125−6014, J1614−2230, and J1909−3744, we determined pulsar masses to be $M_{\\rm p} = 1.68\\pm 0.17$, $1.94\\pm 0.03$, and $1.45 \\pm 0.03 \\, {\\rm M_{\\odot }}$, and companion masses to be $M_{\\rm c} = 0.33\\pm 0.02$, $0.495\\pm 0.005$, and $0.205 \\pm 0.003 \\, {\\rm M_{\\odot }}$, respectively. This provides the first independent confirmation of PSR J1614−2230’s mass, one of the highest known. The Shapiro delays measured for PSRs J0101−6422, J1101−6424, J1514−4946, and J1732−5049 were only weak, and could not provide interesting component mass limits. Despite a large number of MSPs being routinely timed, relatively few have accurate masses via Shapiro delays. We use simulations to show that this is expected, and provide a formula for observers to assess how accurately a pulsar mass can be determined. We also discuss the observed correlation between pulsar companion masses and spin period, and the anticorrelation between recycled pulsar mass and their companion masses.
Publisher: American Astronomical Society
Date: 09-2020
Abstract: When galaxies merge, the supermassive black holes in their centers may form binaries and emit low-frequency gravitational radiation in the process. In this paper, we consider the galaxy 3C 66B, which was used as the target of the first multimessenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational-wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C 66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C 66B to less than (1.65 ± 0.02) × 10 9 M ⊙ using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data over “blind” pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences.
Publisher: American Astronomical Society
Date: 24-11-2020
Publisher: American Astronomical Society
Date: 02-2023
Abstract: In 2018 an ultra–wide-bandwidth low-frequency (UWL) receiver was installed on the 64 m Parkes Radio Telescope, enabling observations with an instantaneous frequency coverage from 704 to 4032 MHz. Here we present the analysis of a 3 yr data set of 35 ms pulsars observed with the UWL by the Parkes Pulsar Timing Array, using wide-band timing methods. The two key differences compared to typical narrowband methods are (1) generation of two-dimensional templates accounting for pulse shape evolution with frequency and (2) simultaneous measurements of the pulse time of arrival (TOA) and dispersion measure (DM). This is the first time that wide-band timing has been applied to a uniform data set collected with a single large fractional bandwidth receiver, for which such techniques were originally developed. As a result of our study, we present a set of profile evolution models and new timing solutions, including initial noise analysis. Precision of our TOA and DM measurements is in the range of 0.005–2.08 μ s and (0.043–14.24) × 10 −4 cm −3 pc, respectively, with 94% of the pulsars achieving a median TOA uncertainty of less than 1 μ s.
Publisher: American Astronomical Society
Date: 18-02-2020
Publisher: American Astronomical Society
Date: 29-05-2018
Publisher: American Astronomical Society
Date: 25-11-2020
Publisher: Oxford University Press (OUP)
Date: 12-10-2019
Abstract: In this paper, we describe the International Pulsar Timing Array second data release, which includes recent pulsar timing data obtained by three regional consortia: the European Pulsar Timing Array, the North American Nanohertz Observatory for Gravitational Waves, and the Parkes Pulsar Timing Array. We analyse and where possible combine high-precision timing data for 65 millisecond pulsars which are regularly observed by these groups. A basic noise analysis, including the processes which are both correlated and uncorrelated in time, provides noise models and timing ephemerides for the pulsars. We find that the timing precisions of pulsars are generally improved compared to the previous data release, mainly due to the addition of new data in the combination. The main purpose of this work is to create the most up-to-date IPTA data release. These data are publicly available for searches for low-frequency gravitational waves and other pulsar science.
Publisher: American Astronomical Society
Date: 10-2023
Publisher: Oxford University Press (OUP)
Date: 24-12-2017
Publisher: Oxford University Press (OUP)
Date: 27-06-2020
Abstract: The SUrvey for Pulsars and Extragalactic Radio Bursts ran from 2014 April to 2019 August, covering a large fraction of the Southern hemisphere at mid- to high-galactic latitudes and consisting of 9-min pointings taken with the 20-cm multibeam receiver on the Parkes Radio Telescope. Data up to 2017 September 21 have been searched using standard Fourier techniques, single-pulse searches, and Fast Folding Algorithm searches. We present 19 new discoveries, bringing the total to 27 discoveries in the programme, and we report the results of follow-up timing observations at Parkes for 26 of these pulsars, including the millisecond pulsar PSR J1421−4409 the faint, highly modulated, slow pulsar PSR J1646−1910 and the nulling pulsar PSR J1337−4441. We present new timing solutions for 23 pulsars, and we report flux densities, modulation indices, and polarization properties.
Publisher: American Astronomical Society
Date: 29-06-2023
Abstract: Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial correlation. Here we describe a search for an isotropic stochastic gravitational-wave background (GWB) using observations of 30 millisecond pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA), which spans 18 yr. Using current Bayesian inference techniques we recover and characterize a common-spectrum noise process. Represented as a strain spectrum h c = A ( f / 1 yr − 1 ) α , we measure A = 3.1 − 0.9 + 1.3 × 10 − 15 and α = −0.45 ± 0.20, respectively (median and 68% credible interval). For a spectral index of α = −2/3, corresponding to an isotropic background of GWs radiated by inspiraling supermassive black hole binaries, we recover an litude of A = 2.04 − 0.22 + 0.25 × 10 − 15 . However, we demonstrate that the apparent signal strength is time-dependent, as the first half of our data set can be used to place an upper limit on A that is in tension with the inferred common-spectrum litude using the complete data set. We search for spatial correlations in the observations by hierarchically analyzing in idual pulsar pairs, which also allows for significance validation through randomizing pulsar positions on the sky. For a process with α = −2/3, we measure spatial correlations consistent with a GWB, with an estimated false-alarm probability of p ≲ 0.02 (approx. 2 σ ). The long timing baselines of the PPTA and the access to southern pulsars will continue to play an important role in the International Pulsar Timing Array.
Publisher: Oxford University Press (OUP)
Date: 07-12-2017
Publisher: Oxford University Press (OUP)
Date: 19-08-2020
Abstract: The millisecond pulsar J1823−3021A is a very active giant pulse emitter in the globular cluster NGC 6624. New observations with the MeerKAT radio telescope have revealed 14350 giant pulses over 5 h of integration time, with an average wait time of about 1 s between giant pulses. The giant pulses occur in phases compatible with the ordinary radio emission, follow a power-law distribution with an index of −2.63 ± 0.02, and contribute 4 per cent of the total integrated flux. The spectral index of the giant pulses follows a Gaussian distribution centred around −1.9 with a standard deviation of 0.6 and is on average flatter than the integrated emission, which has a spectral index of −2.81 ± 0.02. The waiting times between the GPs are accurately described by a Poissonian distribution, suggesting that the time of occurrence of a GP is independent from the times of occurrence of other GPs. 76 GPs show multiple peaks within the same rotation, a rate that is also compatible with the mutual independence of the GP times of occurrence. We studied the polarization properties of the giant pulses finding, on average, linear polarization only at the 1 per cent level and circular polarization at the 3 per cent level, similar to the polarization percentages of the total integrated emission. In four cases, it was possible to measure the RM of the GPs that are highly variable and, in two cases, is inconsistent with the mean RM of the total integrated pulsar signal.
Publisher: American Astronomical Society
Date: 12-2020
Publisher: Oxford University Press (OUP)
Date: 02-12-2020
Abstract: Cosmic strings are potential gravitational-wave (GW) sources that can be probed by pulsar timing arrays (PTAs). In this work we develop a detection algorithm for a GW burst from a cusp on a cosmic string, and apply it to Parkes PTA data. We find four events with a false alarm probability less than 1 per cent. However further investigation shows that all of these are likely to be spurious. As there are no convincing detections we place upper limits on the GW litude for different event durations. From these bounds we place limits on the cosmic string tension of Gμ ∼ 10−5, and highlight that this bound is independent from those obtained using other techniques. We discuss the physical implications of our results and the prospect of probing cosmic strings in the era of Square Kilometre Array.
Publisher: American Astronomical Society
Date: 09-04-2018
Publisher: American Astronomical Society
Date: 08-04-2020
Publisher: American Astronomical Society
Date: 21-04-2020
Publisher: American Astronomical Society
Date: 20-03-0031
Publisher: Oxford University Press (OUP)
Date: 04-11-2019
Abstract: We have constructed a new time-scale, TT(IPTA16), based on observations of radio pulsars presented in the first data release from the International Pulsar Timing Array (IPTA). We used two analysis techniques with independent estimates of the noise models for the pulsar observations and different algorithms for obtaining the pulsar time-scale. The two analyses agree within the estimated uncertainties and both agree with TT(BIPM17), a post-corrected time-scale produced by the Bureau International des Poids et Mesures (BIPM). We show that both methods could detect significant errors in TT(BIPM17) if they were present. We estimate the stability of the atomic clocks from which TT(BIPM17) is derived using observations of four rubidium fountain clocks at the US Naval Observatory. Comparing the power spectrum of TT(IPTA16) with that of these fountain clocks suggests that pulsar-based time-scales are unlikely to contribute to the stability of the best time-scales over the next decade, but they will remain a valuable independent check on atomic time-scales. We also find that the stability of the pulsar-based time-scale is likely to be limited by our knowledge of solar-system dynamics, and that errors in TT(BIPM17) will not be a limiting factor for the primary goal of the IPTA, which is to search for the signatures of nano-Hertz gravitational waves.
Publisher: American Astronomical Society
Date: 24-04-2018
Publisher: Oxford University Press (OUP)
Date: 28-06-2019
Abstract: The Parkes Pulsar Timing Array (PPTA) project monitors two dozen millisecond pulsars (MSPs) in order to undertake a variety of fundamental physics experiments using the Parkes 64-m radio telescope. Since 2017 June, we have been undertaking commensal searches for fast radio bursts (FRBs) during the MSP observations. Here, we report the discovery of four FRBs (171209, 180309, 180311, and 180714). The detected events include an FRB with the highest signal-to-noise ratio ever detected at the Parkes Observatory, which exhibits unusual spectral properties. All four FRBs are highly polarized. We discuss the future of commensal searches for FRBs at Parkes.
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.19
Abstract: MeerTime is a five-year Large Survey Project to time pulsars with MeerKAT, the 64-dish South African precursor to the Square Kilometre Array. The science goals for the programme include timing millisecond pulsar (MSPs) to high precision ( ${ } 1 \\unicode{x03BC} \\mathrm{s}$ ) to study the Galactic MSP population and to contribute to global efforts to detect nanohertz gravitational waves with the International Pulsar Timing Array (IPTA). In order to plan for the remainder of the programme and to use the allocated time most efficiently, we have conducted an initial census with the MeerKAT ‘ L -band’ receiver of 189 MSPs visible to MeerKAT and here present their dispersion measures, polarisation profiles, polarisation fractions, rotation measures, flux density measurements, spectral indices, and timing potential. As all of these observations are taken with the same instrument (which uses coherent dedispersion, interferometric polarisation calibration techniques, and a uniform flux scale), they present an excellent resource for population studies. We used wideband pulse portraits as timing standards for each MSP and demonstrated that the MeerTime Pulsar Timing Array (MPTA) can already contribute significantly to the IPTA as it currently achieves better than $1\\,\\unicode{x03BC}\\mathrm{s}$ timing accuracy on 89 MSPs (observed with fortnightly cadence). By the conclusion of the initial five-year MeerTime programme in 2024 July, the MPTA will be extremely significant in global efforts to detect the gravitational wave background with a contribution to the detection statistic comparable to other long-standing timing programmes.
Publisher: American Astronomical Society
Date: 08-2021
Publisher: American Astronomical Society
Date: 02-2023
Abstract: We present timing solutions for 12 pulsars discovered in the Green Bank North Celestial Cap 350 MHz pulsar survey, including six millisecond pulsars (MSPs), a double neutron star (DNS) system, and a pulsar orbiting a massive white dwarf companion. Timing solutions presented here include 350 and 820 MHz Green Bank Telescope data from initial confirmation and follow-up, as well as a dedicated timing c aign spanning 1 ryr PSR J1122−3546 is an isolated MSP, PSRs J1221−0633 and J1317−0157 are MSPs in black widow systems and regularly exhibit eclipses, and PSRs J2022+2534 and J2039−3616 are MSPs that can be timed with high precision and have been included in pulsar timing array experiments seeking to detect low-frequency gravitational waves. PSRs J1221−0633 and J2039−3616 have Fermi Large Area Telescope gamma-ray counterparts and also exhibit significant gamma-ray pulsations. We measure proper motions for three of the MSPs in this s le and estimate their space velocities, which are typical compared to those of other MSPs. We have detected the advance of periastron for PSR J1018−1523 and therefore measure the total mass of the DNS system, m tot = 2.3 ± 0.3 M ⊙ . Long-term pulsar timing with data spanning more than 1 yr is critical for classifying recycled pulsars, carrying out detailed astrometry studies, and shedding light on the wealth of information in these systems post-discovery.
Publisher: American Astronomical Society
Date: 04-2022
Abstract: Using Bayesian analyses we study the solar electron density with the NANOGrav 11 yr pulsar timing array (PTA) data set. Our model of the solar wind is incorporated into a global fit starting from pulse times of arrival. We introduce new tools developed for this global fit, including analytic expressions for solar electron column densities and open source models for the solar wind that port into existing PTA software. We perform an ab initio recovery of various solar wind model parameters. We then demonstrate the richness of information about the solar electron density, n E , that can be gleaned from PTA data, including higher order corrections to the simple 1/ r 2 model associated with a free-streaming wind (which are informative probes of coronal acceleration physics), quarterly binned measurements of n E and a continuous time-varying model for n E spanning approximately one solar cycle period. Finally, we discuss the importance of our model for chromatic noise mitigation in gravitational-wave analyses of pulsar timing data and the potential of developing synergies between sophisticated PTA solar electron density models and those developed by the solar physics community.
Publisher: Oxford University Press (OUP)
Date: 18-03-2021
Abstract: We have used the central 44 antennas of the new 64-dish MeerKAT radio telescope array to conduct a deep search for new pulsars in the core of nine globular clusters (GCs). This has led to the discovery of eight new millisecond pulsars in six different clusters. Two new binaries, 47 Tuc ac and 47 Tuc ad, are eclipsing ‘spiders’, featuring compact orbits (≲0.32 d), very low mass companions, and regular occultations of their pulsed emission. The other three new binary pulsars (NGC 6624G, M62G, and Ter 5 an) are in wider (& .7 d) orbits, with companions that are likely to be white dwarfs or neutron stars. NGC 6624G has a large eccentricity of e ≃ 0.38, which enabled us to detect the rate of advance of periastron. This suggests that the system is massive, with a total mass of Mtot = 2.65 ± 0.07 M⊙. Likewise, for Ter 5 an, with e ≃ 0.0066, we obtain Mtot = 2.97 ± 0.52 M⊙. The other three new discoveries (NGC 6522D, NGC 6624H, and NGC 6752F) are faint isolated pulsars. Finally, we have used the whole MeerKAT array and synthesized 288 beams, covering an area of ∼2 arcmin in radius around the centre of NGC 6624. This has allowed us to localize many of the pulsars in the cluster, demonstrating the beamforming capabilities of the TRAPUM software backend and paving the way for the upcoming MeerKAT GC pulsar survey.
Publisher: Oxford University Press (OUP)
Date: 08-01-2021
Abstract: Using the state-of-the-art SKA precursor, the MeerKAT radio telescope, we explore the limits to precision pulsar timing of millisecond pulsars achievable due to pulse stochasticity (jitter). We report new jitter measurements in 15 of the 29 pulsars in our s le and find that the levels of jitter can vary dramatically between them. For some, like the 2.2 ms pulsar PSR J2241−5236, we measure an implied jitter of just ∼4 ns h−1, while others, like the 3.9 ms PSR J0636−3044, are limited to ∼100 ns h−1. While it is well known that jitter plays a central role to limiting the precision measurements of arrival times for high signal-to-noise ratio observations, its role in the measurement of dispersion measure (DM) has not been reported, particularly in broad-band observations. Using the exceptional sensitivity of MeerKAT, we explored this on the bright millisecond pulsar PSR J0437−4715 by exploring the DM of literally every pulse. We found that the derived single-pulse DMs vary by typically 0.0085 cm−3 pc from the mean, and that the best DM estimate is limited by the differential pulse jitter across the band. We postulate that all millisecond pulsars will have their own limit on DM precision which can only be overcome with longer integrations. Using high-time resolution filterbank data of 9 μs, we also present a statistical analysis of single-pulse phenomenology. Finally, we discuss optimization strategies for the MeerKAT pulsar timing program and its role in the context of the International Pulsar Timing Array.
Publisher: American Astronomical Society
Date: 11-2021
Abstract: The Green Bank North Celestial Cap survey is a 350 MHz all-sky survey for pulsars and fast radio transients using the Robert C. Byrd Green Bank Telescope. To date, the survey has discovered over 190 pulsars, including 33 millisecond pulsars and 24 rotating radio transients. Several exotic pulsars have been discovered in the survey, including PSR J1759+5036, a binary pulsar with a 176 ms spin period in an orbit with a period of 2.04 days, an eccentricity of 0.3, and a projected semi-major axis of 6.8 light seconds. Using seven years of timing data, we are able to measure one post–Keplerian parameter, advance of periastron, which has allowed us to constrain the total system mass to 2.62 ± 0.03 M ⊙ . This constraint, along with the spin period and orbital parameters, suggests that this is a double neutron star system, although we cannot entirely rule out a pulsar-white dwarf binary. This pulsar is only detectable in roughly 45% of observations, most likely due to scintillation. However, additional observations are required to determine whether there may be other contributing effects.
Publisher: American Astronomical Society
Date: 03-04-2019
Publisher: Oxford University Press (OUP)
Date: 10-2018
Publisher: Oxford University Press (OUP)
Date: 08-12-2021
Abstract: We present baseband radio observations of the millisecond pulsar J1909 − 3744, the most precisely timed pulsar, using the MeerKAT telescope as part of the MeerTime pulsar timing array c aign. During a particularly bright scintillation event the pulsar showed strong evidence of pulse mode changing, among the first millisecond pulsars and the shortest duty cycle millisecond pulsar to do so. Two modes appear to be present, with the weak (lower signal-to-noise ratio) mode arriving 9.26 ± 3.94 μs earlier than the strong counterpart. Further, we present a new value of the jitter noise for this pulsar of 8.20 ± 0.14 ns in one hour, finding it to be consistent with previous measurements taken with the MeerKAT (9 ± 3 ns) and Parkes (8.6 ± 0.8 ns) telescopes, but inconsistent with the previously most precise measurement taken with the Green Bank telescope (14 ± 0.5 ns). Timing analysis on the in idual modes is carried out for this pulsar, and we find an approximate $10\\, \\mathrm{per\\,cent}$ improvement in the timing precision is achievable through timing the strong mode only as opposed to the full s le of pulses. By forming a model of the average pulse from templates of the two modes, we time them simultaneously and demonstrate that this timing improvement can also be achieved in regular timing observations. We discuss the impact an improvement of this degree on this pulsar would have on searches for the stochastic gravitational wave background, as well as the impact of a similar improvement on all MeerTime PTA pulsars.
Publisher: Springer Science and Business Media LLC
Date: 26-01-2023
DOI: 10.1038/S41550-022-01874-X
Abstract: Reliable neutron star mass measurements are key to determining the equation of state of cold nuclear matter, but such measurements are rare. Black widows and redbacks are compact binaries consisting of millisecond pulsars and semi-degenerate companion stars. Spectroscopy of the optically bright companions can determine their radial velocities, providing inclination-dependent pulsar mass estimates. Although inclinations can be inferred from subtle features in optical light curves, such estimates may be systematically biased due to incomplete heating models and poorly understood variability. Using data from the Fermi Large Area Telescope, we have searched for gamma-ray eclipses from 49 spider systems, discovering significant eclipses in 7 systems, including the prototypical black widow PSR B1957+20. Gamma-ray eclipses require direct occultation of the pulsar by the companion, and so the detection, or significant exclusion, of a gamma-ray eclipse strictly limits the binary inclination angle, providing new robust, model-independent pulsar mass constraints. For PSR B1957+20, the eclipse implies a much lighter pulsar (1.81 ± 0.07 solar masses) than inferred from optical light curve modelling.
Publisher: American Astronomical Society
Date: 07-2023
Abstract: Pulsar timing array collaborations, such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), are seeking to detect nanohertz gravitational waves emitted by supermassive black hole binaries formed in the aftermath of galaxy mergers. We have searched for continuous waves from in idual circular supermassive black hole binaries using NANOGrav’s recent 12.5 yr data set. We created new methods to accurately model the uncertainties on pulsar distances in our analysis, and we implemented new techniques to account for a common red-noise process in pulsar timing array data sets while searching for deterministic gravitational wave signals, including continuous waves. As we found no evidence for continuous waves in our data, we placed 95% upper limits on the strain litude of continuous waves emitted by these sources. At our most sensitive frequency of 7.65 nHz, we placed a sky-averaged limit of h 0 (6.82 ± 0.35) × 10 −15 , and h 0 (2.66 ± 0.15) × 10 −15 in our most sensitive sky location. Finally, we placed a multimessenger limit of ( 1.41 ± 0.02 ) × 10 9 M ⊙ on the chirp mass of the supermassive black hole binary candidate 3C 66B.
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.36
Abstract: We present the third data release from the Parkes Pulsar Timing Array (PPTA) project. The release contains observations of 32 pulsars obtained using the 64-m Parkes “Murriyang” radio telescope. The data span is up to 18 years with a typical cadence of 3 weeks. This data release is formed by combining an updated version of our second data release with ∼ 3 years of more recent data primarily obtained using an ultra-wide-bandwidth receiver system that operates between 704 and 4032 MHz. We provide calibrated pulse profiles, flux-density dynamic spectra, pulse times of arrival, and initial pulsar timing models. We describe methods for processing such wide-bandwidth observations, and compare this data release with our previous release.
Publisher: American Astronomical Society
Date: 20-02-2019
Publisher: American Astronomical Society
Date: 08-2021
Publisher: American Astronomical Society
Date: 23-05-2018
Publisher: American Astronomical Society
Date: 23-01-2020
Publisher: American Astronomical Society
Date: 02-05-2016
Publisher: American Astronomical Society
Date: 22-05-2020
Publisher: Oxford University Press (OUP)
Date: 16-05-2020
Abstract: A handful of fast radio bursts (FRBs) are now known to repeat. However, the question remains – do they all? We report on an extensive observational c aign with the Australian Square Kilometre Array Pathfinder (ASKAP), Parkes, and Robert C. Byrd Green Bank Telescope, searching for repeat bursts from FRBs detected by the Commensal Real-time ASKAP Fast Transients survey. In 383.2 h of follow-up observations covering 27 FRBs initially detected as single bursts, only two repeat bursts from a single FRB, FRB 171019, were detected, which have been previously reported by Kumar et al. We use simulations of repeating FRBs that allow for clustering in burst arrival times to calculate new estimates for the repetition rate of FRB 171019, finding only slight evidence for incompatibility with the properties of FRB 121102. Our lack of repeat bursts from the remaining FRBs set limits on the model of all bursts being attributable to repeating FRBs. Assuming a reasonable range of repetition behaviour, at most 60 per cent (90 per cent confidence limit) of these FRBs have an intrinsic burst distribution similar to FRB 121102. This result is shown to be robust against different assumptions on the nature of repeating FRB behaviour, and indicates that if indeed all FRBs repeat, the majority must do so very rarely.
Publisher: American Astronomical Society
Date: 02-2022
Abstract: In this work, we present polarization profiles for 23 millisecond pulsars observed at 820 and 1500 MHz with the Green Bank Telescope as part of the NANOGrav pulsar timing array. We calibrate the data using Mueller matrix solutions calculated from observations of PSRs B1929+10 and J1022+1001. We discuss the polarization profiles, which can be used to constrain pulsar emission geometry, and present both the first published radio polarization profiles for nine pulsars and the discovery of very low-intensity average profile components (“microcomponents”) in four pulsars. We obtain the Faraday rotation measures for each pulsar and use them to calculate the Galactic magnetic field parallel to the line of sight for different lines of sight through the interstellar medium. We fit for linear and sinusoidal trends in time in the dispersion measure and Galactic magnetic field and detect magnetic field variations with a period of 1 yr in some pulsars, but overall find that the variations in these parameters are more consistent with a stochastic origin.
Publisher: American Astronomical Society
Date: 30-11-2018
Publisher: Oxford University Press (OUP)
Date: 05-04-2022
Abstract: Using the MeerKAT radio telescope, a series of observations have been conducted to time the known pulsars and search for new pulsars in the globular cluster NGC 6440. As a result, two pulsars have been discovered, NGC 6440G and NGC 6440H, one of which is isolated and the other a non-eclipsing (at frequencies above 962 MHz) ‘Black Widow’, with a very low mass companion (Mc & 0.006 M⊙). It joins the other binary pulsars discovered so far in this cluster that all have low companion masses (Mc & 0.30 M⊙). We present the results of long-term timing solutions obtained using data from both Green Bank and MeerKAT telescopes for these two new pulsars and an analysis of the pulsars NGC 6440C and NGC 6440D. For the isolated pulsar NGC 6440C, we searched for planets using a Markov chain Monte Carlo technique. We find evidence for significant unmodelled variations but they cannot be well modelled as planets nor as part of a power-law red-noise process. Studies of the eclipses of the ‘Redback’ pulsar NGC 6440D at two different frequency bands reveal a frequency dependence with longer and asymmetric eclipses at lower frequencies (962–1283 MHz).
Publisher: Oxford University Press (OUP)
Date: 12-2015
Publisher: Oxford University Press (OUP)
Date: 05-04-2017
DOI: 10.1093/MNRAS/STX837
Publisher: Oxford University Press (OUP)
Date: 19-01-2022
Abstract: We searched for an isotropic stochastic gravitational wave background in the second data release of the International Pulsar Timing Array, a global collaboration synthesizing decadal-length pulsar-timing c aigns in North America, Europe, and Australia. In our reference search for a power-law strain spectrum of the form $h_c = A(f/1\\, \\mathrm{yr}^{-1})^{\\alpha }$, we found strong evidence for a spectrally similar low-frequency stochastic process of litude $A = 3.8^{+6.3}_{-2.5}\\times 10^{-15}$ and spectral index α = −0.5 ± 0.5, where the uncertainties represent 95 per cent credible regions, using information from the auto- and cross-correlation terms between the pulsars in the array. For a spectral index of α = −2/3, as expected from a population of inspiralling supermassive black hole binaries, the recovered litude is $A = 2.8^{+1.2}_{-0.8}\\times 10^{-15}$. None the less, no significant evidence of the Hellings–Downs correlations that would indicate a gravitational-wave origin was found. We also analysed the constituent data from the in idual pulsar timing arrays in a consistent way, and clearly demonstrate that the combined international data set is more sensitive. Furthermore, we demonstrate that this combined data set produces comparable constraints to recent single-array data sets which have more data than the constituent parts of the combination. Future international data releases will deliver increased sensitivity to gravitational wave radiation, and significantly increase the detection probability.
Publisher: American Astronomical Society
Date: 22-08-2016
Publisher: American Astronomical Society
Date: 12-2022
Publisher: American Astronomical Society
Date: 12-07-2018
Publisher: American Astronomical Society
Date: 25-02-2019
Publisher: American Astronomical Society
Date: 20-07-2018
Publisher: American Physical Society (APS)
Date: 31-03-2016
Publisher: American Astronomical Society
Date: 25-07-2016
Publisher: American Astronomical Society
Date: 31-07-2019
Publisher: Oxford University Press (OUP)
Date: 15-02-2016
DOI: 10.1093/MNRAS/STW347
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 11-2015
End Date: 09-2021
Amount: $2,840,752.00
Funder: Australian Research Council
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